1. Field of the Invention
The invention relates to drill chucks for use with electric or pneumatic power drills. More particularly it relates to a chuck of the keyless type which is tightened or loosened by actuation of the drill motor.
2. Prior Art
Electric or pneumatic power tools are commonly provided with tool holders or chucks intended to grip the shank of a tool, such as a drill bit. Usually, the tool holder or chuck is formed with an axial threaded hole adapted to engage the threaded end of the drive shaft of the power tool. Alternatively, the tool holder or chuck may have an axial tapered hole which mates with a tapered drive shaft of the power tool.
A wide variety of chucks has been developed by the art. In the simplest form of chuck three jaws spaced 120.degree. apart from each other are constrained by a conical body threaded onto the drive shaft so that rotation of the body in one direction relative to the drive shaft forces the jaws into gripping relationship with respect to the cylindrical shank of a tool while rotation in the opposite direction releases the gripping relationship. Such a chuck may be a keyless chuck if the body is rotated by hand. However, because the tightening or loosening torque which may be applied directly in a hand operation is limited, the art developed the so-called three jaw geared chuck. This design overcomes the principal problems in the earlier design by providing guideways in the chuck body to control accurately the motion of the jaws and teeth on the jaws which mesh with a gear driven nut mounted on the chuck body. The gear is actuated by a pinion formed on a separate key which may be rotated in a bearing hole formed in the chuck body.
While the three jaw geared chuck is capable of high precision and can exert a considerable gripping force on the tool, it is relatively expensive to manufacture. In addition, the operating key may easily be misplaced and the hand operation required for chucking and unchucking a tool is time consuming.
In order to overcome these perceived disadvantages of the three jaw geared chuck, a number of designs have been proposed in which means are provided to restrain a portion of the chuck while applying power to rotate the drive shaft in a forward or reverse direction. Such relative motion produces a tightening or loosening operation. Stoner U.S. Pat. No. 2,684,856, Hall U.S. Pat. No. 4,260,169 and Whitehead U.S. Pat. No. 4,423,881 disclose keyless chucks in which the outer sleeve of the chuck is held against rotation while the drive shaft is power driven to tighten or loosen the chuck. Moeller U.S. Pat. No. 4,085,337 provides a gear driven mechanism for opening and closing the chuck jaws. The use of dog impact mechanisms appears in Rowe U.S. Pat. No. 2,716,555, Kilberis U.S. Pat. No. 4,277,074, Welch U.S. Pat. No. 4,317,578, Rohlin U.S. Pat. No. 4,358,230, Hatfield U.S. Pat. No. 4,526,497 and Hatfield U.S. Pat. No. 4,536,113. Another approach involves the use of a brake mechanism in which a sleeve or a band is tightened against the chuck sleeve to restrain its movement. This approach appears in Eberhardt U.S. Pat. No. 4,323,324, Sivertson U.S. Pat. No. 4,460,296 and Whitehead U.S. Pat. No. 4,575,108. Finally, the use of a lever or a dog to hold the chuck sleeve stationary is shown in Coder U.S. Pat. No. 4,389,146, Clarey U.S. Pat. No. 4,395,170 and Glore U.S. pat. No. 4,498,682.